The present invention relates to a cation exchanger or chelating agent and a production process thereof. The cation exchanger of the present invention has a novel structure with excellent heat resistance and other features, and the chelating agent of the present invention has a novel structure with excellent chelate forming ability, heat resistance and other features.
Generally, cation exchange resins are produced by sulfonating styrene-divinylbenzene copolymers with sulfuric acid and/or sulfur trioxide of various concentrations in view of chemical stability of the produced resins, their strength and production cost. There are also known the cation exchange resins produced by introducing a sulfonic group to the terminal of acrylic derivative resins, but these cation exchange resins are poor in chemical stability.
As another exemplification of cation exchange resins, in U.S. Pat. No. 3,944,507 specification, there has been described a cation exchanger incorporated with methylene linkage (benzenesulfonic acid structure), but this cation exchanger is unsatisfactory in heat resistance. There has also been described a cation exchanger produced by introducing a halogen atom into the benzene ring for improving heat resistance, but this cation exchanger has not been commercially produced and used because of liability to ion leakage of its halides such as chlorinated or brominated products.
On the other hand, chelating agents (resins) are the functional resins produced by introducing functional groups capable of forming metal ions and chelates to the crosslinked polymers, and a variety of chelate resins have been proposed according to the type of the chelate-forming functional group used. Typical examples of the chelate-forming functional groups usable for the above purpose are iminodiacetic acid group (xe2x80x94N(CH2COOxe2x80x94)2) and polyamine group (xe2x80x94NH(CH2CH2NH)n.H). These chelate resins, for example, the said iminodiacetic acid type chelate resins are usually produced by converting the halogen of a crosslinked polymer containing halogenated methylstyrene into iminodiacetic acid group.
It appears, however, that most of the conventional proposals relating to chelate resins are directed to the improvement of chelate-forming functional groups and no sufficient proposals have been made on the structure between the crosslinked polymer and the chelate-forming functional group.
The present invention has been made in view of the above circumstances, and an object thereof is to provide a cation exchanger which has excellent heat resistance and high reaction rate, is capable of minimized elution from the polymer, and a process for producing such a cation exchanger. Another object of the present invention is to provide a chelating agent of a novel structure having excellent chelate forming ability and heat resistance, and a process for producing such a chelating agent.
An object of the present invention can be attained by a cation exchanger or a chelating agent having at least structural units represented by the following formula (I), the structural units being derived from a crosslinkable monomer containing an unsaturated hydrocarbon group: 
wherein A represents a C3-C8 alkylene group or a C4-C9 alkoxymethylene group; L represents SO3xe2x88x92X+, where X+ is a counter ion coordinated with the SO3xe2x88x92 group, or a chelate-forming functional group; and the benzene ring may be substituted with an alkyl group or a halogen atom.
Another object of the present invention can be accomplished by a process for producing a cation exchanger as defined in the above first aspect, which comprises suspension-polymerizing at least a precursor monomer having the structural units represented by the following formula (II) and a crosslinkable monomer having an unsaturated hydrocarbon group in the presence of a polymerization initiator, and if necessary introducing a cation exchange group into the obtained spherical crosslinked polymer: 
wherein A has the same meaning as defined in the formula (I); Z1 represents chlorine, bromine, iodine, a hydroxyl group, a tosyl group (toluenesulfonic group), a thiol group or a sulfonic group; and the benzene ring may be substituted with an alkyl group or a halogen atom.
Still another object of the present invention can be achieved by a process for producing a chelating agent as defined in the above first aspect, which comprises suspension-polymerizing at least a precursor monomer having the structural units represented by the following formula (III) and a crosslinkable monomer having an unsaturated hydrocarbon group in the presence of a polymerization initiator, and introducing a chelate-forming functional group into the obtained spherical crosslinked polymer: 
wherein A has the same meaning as defined in the formula (I); Z2 represents chlorine, bromine; iodine or a hydroxyl group; and the benzene ring may be substituted with an alkyl group or a halogen atom.
The present invention is described in detail below.
First, the cation exchanger or chelating agent according to the present invention is explained.
The cation exchanger or chelating agent of the present invention has at least the structural units represented by the above-shown formula (I) and the structural units derived from a crosslinkable monomer having an unsaturated hydrocarbon group.
In case where L in the formula (I) is SO3xe2x88x92Xxe2x88x92 (wherein X+ is a counter ion coordinated with the SO3xe2x88x92 group), a cation exchanger is provided; and in case where L is a chelate-forming functional group, a chelating agent is provided.
L representing a chelate-forming functional group is not specified, and any functional group used in the known chelate resins can be used without restrictions. Typical examples of L include iminodiacetate group (xe2x80x94N(CH2COOxe2x80x94)2), polyamine group (xe2x80x94NH(CH2CH2NH)n.H), dimethylglycine (dimethylaminoacetate) group (xe2x80x94N+(CH3)2CH2COOxe2x80x94) and the like. As compared with, for example, aminomethylsulfonic group disclosed in Japanese Patent KOHYO (Laid-Open PCT Application) No. 4-500223, it is particularly remarkable that these chelate-forming functional groups, are relatively simple in structure, advantageous in cost and also susceptible to the influence of benzene ring because of relatively simple molecular structure, so that the effect by spacer (A) in the present invention, which is described later, is remarkable.
Besides the above-mentioned, there can also be used aminophosphoric group and phosphonic group as the chelate-forming functional group. The aminophosphoric type chelate resins can, for instance, be preferably used for purification of salt water contained in the raw materials of electrolytic sodium hydroxide and are capable of effectively removing the impurities such as calcium and strontium in the salt water. On the other hand, the phosphonic type chelate resins show high adsorptivity for many types of metal ions and have higher selectivity for tri- and tetravalent metal ions than for mono- and divalent metal ions. Because of these properties, the phosphonic chelate resins are advantageously used for selective removal of iron ions in zinc or nickel electroplating solutions and for separation and concentration of uranium and rare earth element ions.
In the formula (I), A represents an alkylene group having 3 to 8 carbon atoms or an alkoxymethylene group having 4 to 9 carbon atoms. Examples of the C3-C8 alkylene groups include propylene, butylene, pentylene, hexylene and octylene, and examples of the C4-C9 alkoxymethylene groups include butoxymethylene and pentoxymethylene. The C3-C8 alkylene groups may be either straight-chain alkylene groups such as mentioned above or branched alkylene groups such as isopropyl and t-butyl groups. When A is an alkylene group, it is preferably a straight-chain alkylene group having 3 to 8 carbon atoms, more preferably the one having 3 to 6 carbon atoms. When A is an alkoxymethylene group, it is preferably the one having 5 to 7 carbon atoms.
Japanese Patent KOHYO (Laid-Open PCT Application) No. 4-500223 has proposed a process for producing aminomethylphosphonic chelate resins by introducing a functional group represented by the formula xe2x80x94(CHR1)mxe2x80x94NR2xe2x80x94CH2xe2x80x94PO3R3R4 (wherein R1 includes hydrogen and m is a number of 1 to 12) into a crosslinked polymer. However, the chelate resins described concretely in the above patent, for example, the chelate resins mentioned in all of the Examples 1-27 are the ones obtainable by introducing an aminomethylphosphonic group into a chloromethylated crosslinked polymer which is a compound of the formula (I) wherein m is 1.
In the present invention, when A does not satisfy the above definition, there are the following problems for both of cation exchanger and chelating agent.
When A is a Short-Chain Group Like Methylene or Ethylene
(1) Cation exchange group (SO3xe2x88x92 group) is subject to the influence of benzene ring through the short chain, and consequently no satisfactory heat resistance may be obtained and also acidity lowers. Reduction of acidity can well be anticipated from the fact that alkylsulfonic acid has higher acidity than benzenesulfonic acid and also aliphatic carboxylic acids have higher acidity than benzoic acid.
(2) The chelate-forming functional group may not fully show its chelate forming ability because its free movement is restricted. Also, as the chelate-forming functional group is subject to the influence of benzene ring through the short chain, no satisfactory heat resistance may be obtained.
When A is a Long-Chain Group Like Nonylene
(1) Molecular weight of the cation exchanger is enlarged, so that the ion exchange capacity per unit weight may be reduced.
(2) Long chain is advantageous from the viewpoint of improvement of chelate forming ability, but the molecular weight of chelate resin is enlarged, so that the chelate forming ability per unit weight may be reduced.
In the present invention, it is preferable for production of the objective substance that A is introduced to the m- or p-position of the styrene residue. Although little influence is expected to be given to the steric relation between benzene ring and substituent group (L being SO3xe2x88x92 group or chelate- forming functional group) even when A is introduced to the opposition, it is preferable to introduce A to the m- or p-position in consideration of possible steric hindrance in copolymerization with a crosslinking agent.
The alkyl groups which may substitute the benzene ring include methyl and ethyl, and the substituent halogen atoms include fluorine, chlorine, bromine and iodine.
Examples of the crosslinkable monomers having unsaturated hydrocarbon groups include divinylbenzene, polyvinylbenzene, alkyldivinylbenzene, dialkyldivinylbenzene, ethylene glycol (poly)(meth)acrylate, polyethylene glycol di(meth)acrylate, (poly)ethylenebis(meth)acrylamide, and the like of these monomers, divinylbenzene is preferred.
In the cation exchanger or chelating agent of the present invention, the percentages of the structural units represented by the formula (I) and the structural units derived from a crosslinkable monomer having an unsaturated hydrocarbon group are not specifically defined. It is notable, however, that a too small ratio of the structural units represented by the formula (I) leads to a reduction of ion exchange capacity or chelating ability (exchange capacity) per unit weight, while a too small percentage of the structural units derived from a crosslinkable monomer having an unsaturated hydrocarbon group results in a high swelling tendency to cause a decrease of ion exchange capacity or chelating ability (exchange capacity) per unit weight. Therefore, the percentages of the respective structural units should be properly selected by taking into account ion exchange capacity, chelating ability (exchange capacity), swelling tendency, strength and other factors.
It is, however, preferable that the percentage of the structural units (precursor monomer) represented by the formula (I) in the whole structural units (whole precursor monomers) constituting the cation exchanger or chelating agent is usually 5 to 99 mol %, preferably 50 to 99 mol %, and the percentage of the structural units (precursor monomer) derived from a crosslinkable monomer having an unsaturated hydrocarbon group is usually 0.1 to 50 mol %, preferably 0.2 to 25 mol %.
The neutral salt decomposition capacity per unit weight of the cation exchanger of the present invention is usually 1.0 to 6.0 meq/g, preferably 1.0 to 5.5 meq/g, and its ion exchange capacity per unit weight, although variable depending on the water content, is usually 0.1 to 2.1 meq/ml. Here, the symbol xe2x80x9cmeq/gxe2x80x9d denotes milliequivalent per unit weight of dry resin, the symbol xe2x80x9cmeq/mlxe2x80x9d denotes milliequivalent per unit volume of hydrous resin.
The exchange capacity per unit weight of the chelate resin of the present invention is usually 1.0 to 6.0 meq/g, preferably 1.0 to 5.5 meq/g, and its exchange capacity per unit volume, although variable depending on water content, is usually 0.1 to 2.1 meq/g. Here, the symbol xe2x80x9cmeq/gxe2x80x9d denotes milliequivalent per unit weight of dry resin, and the symbol xe2x80x9cmeq/mlxe2x80x9d denotes milliequivalent per unit volume of hydrous resin.
Next, a process for producing the cation exchanger according to the present invention is described.
The cation exchanger of the present invention can be produced by suspension polymerizing at least a precursor monomer having the structural units represented by the formula (II) and a crosslinkable monomer having an unsaturated hydrocarbon group in the presence of a polymerization initiator, and if necessary introducing a cation exchange group into the obtained spherical crosslinked polymer.
The structural unit represented by the formula (II) is a precursor of the structural unit represented by the formula (I) (where L is SO3xe2x88x92X+). In the formula (II), A has the same meaning as defined in the formula (I), Z1 represents chlorine, bromine, iodine, a hydroxyl group, a tosyl group (toluenesulfonic group), a thiol group or a sulfonic group, and the benzene ring may be substituted with an alkyl group or a halogen atom. Introduction of a cation exchange group is required in case where Z1 is a substituent group other than sulfonic group.
The precursor monomers of the structural units represented by the formula (II) where A is an alkylene group (alkyl spacer type monomers) can be synthesized, for example, in the following way: a halogenated styrene (such as chlorostyrene or bromostyrene), a chloromethylstyrene (which may be a mixture of m-form and p-form) or a vinylphenetyl halide is reacted with a metallic magnesium to obtain a Grignard reagent and the latter is coupled with 1, xcfx89-dihalogenoalkane.
In the coupling reaction, a catalyst such as a copper halide (copper chloride, copper bromide or copper iodide), Li2CuCl4 or an amine may be used to carry out the reaction efficiently. An alkyl spacer type monomer can also be synthesized by a method in which a xcfx89-halogenoalkylbenzene derivative is acetylated and then a vinyl group is introduced.
The precursor monomers of the structural units represented by the formula (II) where A is an alkoxymethylene group (ether spacer type monomers) can be synthesized, for example, in the following way: a vinylbenzyl alcohol is reacted with 1, xcfx89-dihalogenoalkane to convert into a halogenoalkoxymethylstyrene derivative.
Suspension polymerization is carried out with a suspension containing a precursor monomer of the structural units represented by the formula (II) and a crosslinkable monomer having an unsaturated hydrocarbon group. In this case, if necessary a third monomer may be used as a copolymerization component within limits not lowering the function of the produced cation exchanger of the present invention.
As the copolymerization component, there can be used, for example, styrene, alkylstyrene, polyalkylstyrene, (meth)acrylic ester, (meth)acrylic acid, acrylonitrile and the like, in an amount of usually not more than 50 mol %, preferably not more than 20 mol %, based on the total amount of the essential monomers. The byproducts in the synthesis of the precursor monomers of the structural units represented by the formula (II), such as bisvinylphenylethane, bisvinybenzylether and bisvinylphenylbutane, can also be used as crosslinking agent.
A known water-in-oil type or oil-in-water type suspension polymerization method can be employed for the suspension polymerization in the present invention. In this suspension polymerization, the bath ratio of water to oil or oil to water is preferably adjusted to fall in the range from 1:2 to 1:6. As the polymerization initiator, there can be used any pertinent type of polymerization initiators such as peroxide type and azo type, specifically such peroxide type polymerization initiators as benzoyl peroxide (BPO), lauroyl peroxide and t-butyl hydroperoxide, and such azo type polymerization initiators as azoisobutylnitrile (AIBN) and 2,2xe2x80x2-azobis(2,4-dimethylvaleronitrile).
The amount of the polymerization initiator used for the reaction is usually 0.1 to 3 wt % based on the overall amount of the monomers. Polymerization temperature depends on half-value period temperature and content of the polymerization initiator used, polymerizability of the monomers and other factors, but is usually 40 to 150xc2x0 C., preferably 50 to 100xc2x0 C. Polymerization time is usually one to 30 hours, preferably one to 15 hours.
In the suspension polymerization, various types of solvent may be added as required. The physical structure of the obtained crosslinked copolymer particles differs depending on the kind and amount of the solvent used, so that it is possible to obtain the preferred type, such as gel type or porous type, of crosslinked copolymer particles by controlling the solvent used.
For instance, in case where suspension polymerization is carried out by adding an organic solvent such as toluene, hexane, isooctane, 2-ethylhexanol or the like which is a poor solvent for the precursor monomers of the structural units represented by the formula (II), there can be obtained the crosslinked copolymer particles of a porous structure although the product is variable depending on the monomer content in the suspension polymerization system. On the other hand, in case where a good solvent such as tetrahydrofuran, 1,4-dioxane or the like is used, there can be obtained the crosslinked copolymer particles with a swelling tendency. It is also possible to add other types of solvent such as water, methanol, ethanol, acetone or the like. The amount of such a solvent added is usually not more than 200 wt % based on the total amount of the monomers.
The size of the obtained crosslinked polymer particles may differ in a manner according to the purpose of use of the cation exchanger. In case where it is used as an ion exchange resin, the average particle size is usually 50 xcexcm to 2 mm, and in case where it is used as a resin for catalysts, the average particle size is usually 20 xcexcm to 1 mm.
In the production process of the present invention, in case where Z1 in the formula (II) is a substituent group other than sulfonic group, a cation exchange group (sulfonic group in the formula (II)) is introduced by a known method (sulfonation reaction). Such sulfonation reaction can be effected, for example, by the following methods when Z1 is a halogen atom:
(1) The polymerization product is reacted with thiourea to obtain an isothiouronium salt and then the product is oxidized with hydrogen peroxide or the like to convert the substituent into sulfonic group.
(2) The polymerization product is reacted with EtOCS2K to obtain a dithiocarbonic acid-O-ethyl ester and then the product is oxidized to convert the substituent into sulfonic group.
(3) The polymerization product is reacted with CH3COSH to obtain an acetic thioester and then the product is oxidized to covert the substituent into sulfonic group.
(4) In case where Z1 for introducing a sulfonic group through reaction with sodium sulfite is a thiol group, the polymerization product may be oxidized to convert the substituent into sulfonic group.
In the above reaction, usually a solvent is added to the reaction system for swelling the crosslinked polymer particles. As the solvent, there can be used, for example, water, alcohols such as methanol, ethanol and propanol, hydrocarbons such as toluene and hexane, chlorine type hydrocarbons such as dichloromethane and 1,2-dichloroethane, ethers such as dibutyl ether, dioxane and tetrahydrofuran, and others such as dimethylformamide and acetonitrile. Reaction temperature depends on the mode of reaction, the kind of the functional group and solvent used and other factors, but is usually 20 to 130xc2x0 C.
The cation exchanger of the present invention is obtained in spherical form because of use of suspension polymerization described above, but the product may be pulverized into powders. It is also possible to obtain the product in various other forms such as lumpy, fibrous, filmy, etc., by using solution polymerization.
Besides the above-described monomer method, the cation exchanger of the present invention can also be produced by a method in which a chloromethylated crosslinked copolymer is used as starting material and the substituent group A is introduced by polymeric modification method. More specifically, a method can be used in which a reagent such as n-BuLi is acted to a chloromethylated crosslinked polystyrene to produce the vinylbenzyl anions and the said anion are reacted with 1, xcfx89-dihalogenoalkane to obtain an alkyl spacer type crosslinked copolymer. According to the same method as described in the above, the introduction of sulfonic group can be conducted. However, the above-described monomer method is preferred because of higher ion exchange capacity of the obtained cation exchanger.
Now, a process for producing the chelating agent according to the present invention is explained. The chelating agent of the present invention can be produced by suspension polymerizing a precursor monomer comprising the structural units represented by the formula (III) and a crosslinkable monomer having an unsaturated hydrocarbon group in the presence of a polymerization initiator, and introducing a chelate-forming functional group into the obtained spherical crosslinked polymer. The precursor monomer of the structural units represented by the formula (III) is a precursor of the monomer of the structural units represented by the formula (I) (where L is a chelate-forming functional group). In the formula (III), A has the same meaning as defined in the formula (I), Z2 represents chlorine, bromine, iodine or a hydroxyl group, and the benzene ring may be substituted with an alkyl group or a halogen atom.
In the process for producing the chelating agent, there are used the same monomer method and polymeric modification method as explained in the above-described process for producing the cation exchanger, and the same conditions can be used except for introduction of a chelate-forming functional group in place of a cation exchange group. That is, in the monomer method, the operations till suspension polymerization can be conducted in the completely same way as in the above-described process for producing the cation exchanger to obtain the crosslinked polymer particles. In this case, the average size of the crosslinked polymer particles is usually in the range of 50 xcexcm to 2 mm.
Introduction of the chelate-forming functional group into the spherical crosslinked polymer can be accomplished according to a conventional method. For instance, in case where Z2 is a halogen atom, a dimethylglycine type chelate resin can be obtained by reacting a dimethylglycine ester and hydrolyzing the reaction product. Similarly, an iminodiacetate type chelate resin can be obtained by reacting an iminodiacetic ester and hydrolyzing the reaction product. In case where Z2 is a hydroxyl group, it is also possible to introduce various kinds of chelate-forming functional group into the spherical crosslinked polymer according to a known reaction scheme.
In the above reaction, usually a solvent is added to the reaction system for bloating the crosslinked polymer particles. As the solvent, there can be used those used in the sulfonation reaction described above. Reaction temperature is variable depending on the mode of reaction, the kind of the functional group and solvent used and other factors, but it is usually 20 to 130xc2x0 C.
Introduction of a chelate-forming functional group can be accomplished in the same way as in case where the polymeric modification method is used. The monomer method is preferred to the polymeric modification method as in the case of the cation exchanger.
The chelating agent of the present invention is obtained as a spherical product when using suspension polymerization as in the above-described embodiment, but it may be pulverized into powders. It is also possible to obtain the agent in various other forms, such as lumpy, fibrous, filmy, etc., by using solution polymerization.
According to the present invention, as described above, there is provided a cation exchanger or a chelating agent of a novel structure.
The cation exchanger of the present invention finds a wide range of use. The common uses thereof are, for instance, general-purpose water treatments (softening of hard water, production of pure water, recovery and separation of metals, purification of amino-acids, etc.), separation and purification of saccharic solutions, purification of pharmaceuticals, adsorption removal of colloidal substances such as iron, dehydration, and separation and purification of weakly acidic substances. Among other uses is preparation of various types of adsorbents, such as those for chromatographic carriers, film materials, catalyst carriers, phase-transfer catalysts, enzymes, cells, bacterial cell immobilization carriers, etc. It is especially remarkable that thanks to its excellent heat resistance, the cation exchanger of the present invention is particularly advantageous for use at high temperatures, for instance, in use as a catalyst.
Further, the cation exchanger of the present invention, as apparent from the Examples described below, has the advantage of being minimized in elution from resins, which is a defect of the conventional cation exchangers, and hence almost free of offensive smell.
On the other hand, the chelating agent of the present invention is capable of capturing a wide variety of metallic ions by proper selection of the chelate-forming functional group.
Furthermore, the chelating agent of the present invention has excellent chelate forming ability and heat resistance as well as the advantage of being minimized in elution from resins and hence almost free of offensive smell.